1. Field of the Invention
This invention relates to dislocation free high quality epitaxially grown templates with relaxed lattice constants by using spatially restricted misfit dislocations (MDs) around heterointerfaces, wherein the template layer can be used for epitaxial growth of high In/Al composition devices, such as ultraviolet (UV), green, amber, or red Light Emitting Diodes (LEDs) and green or UV Laser Diodes (LDs).
2. Description of the Related Art
So far, all nitride-based devices are typically grown coherently because dislocations which pass through device layers cause poor device performance. For example, if InGaN is grown coherently on GaN, i.e. without MDs, the in-plane lattice constant of InGaN is constrained to the same value as GaN, which means InGaN layers suffer from compressive in-plane strain (for the case of coherent growth of AlGaN on GaN, the AlGaN epitaxial layer suffers from tensile in-plane strain due to the difference of respective lattice constants).
An approach to reducing or possibly eliminating the polarization effects in GaN optoelectronic devices is to grow the devices on semi-polar planes of the crystal. The term “semi-polar planes” can be used to refer to a wide variety of planes that possess both two nonzero h, i, or k Miller indices and a nonzero 1 Miller index. Thus, semipolar planes are defined as crystal planes with nonzero h or k or i index and a nonzero/index in the (hkil) Miller-Bravais indexing convention. Some commonly observed examples of semi-polar planes in c-plane GaN heteroepitaxy include the (11-22), (10-11), and (10-13) planes, which are found in the facets of pits. These planes also happen to be the same planes that the inventors have grown in the form of planar films. Other examples of semi-polar planes in the wurtzite crystal structure include, but are not limited to, (10-12), (20-21), and (10-14). The nitride crystal's polarization vector lies neither within such planes or normal to such planes, but rather lies at some angle inclined relative to the plane's surface normal. For example, the (10-11) and (10-13) planes are at 62.98° and 32.06° to the c-plane, respectively.